Curling of Brown Leaves & Buds on an Oakleaf Hydrangea

Hydrangeas tend to be fairly resistant to pests and diseases, some do exist that can cause problems for your shrub. The oakleaf hydrangea (Hydrangea quercifolia), which grows in U.S. Department of Agriculture hardiness zones 5 through 9, might develop brown or curling leaves and buds through infestations from a couple of pests or from a fungal infection.

Aphids

Tiny aphids can create a big problem for your oakleaf hydrangea when too many of them decide to make the plant their home. They tend to cluster on the underside of leaves to drink the sap. This can make the leaves curl or pucker and turn yellow or brown. When the infestation gets larger, the blossoms can also be affected, dying before they get a chance to fully bloom. Spraying sharp bursts of water on the plant can wash off the pests, or you can use an insecticidal soap designed to kill aphids.

Root Rot

Root rot is a fungal infection that enters the plant through the roots, especially when the soil is overly wet. All hydrangeas need well-drained soil, but oakleaf hydrangeas are particularly susceptible to root rot. The first sign of root rot is usually entire branches -- blooms and leaves -- turning brown, curling up and falling off the plant. It often happens on one side first, then spreads throughout the plant as the fungus spreads through the roots. Exposing the roots and scraping the outer layer can help you diagnose the problem. If the roots have white, healthy flesh, there's no root rot, but if they are dark and diseased, the fungus has already set in. Fungicides aren't helpful against root rot, but digging up the oakleaf hydrangea and disposing of it in a plastic bag can help prevent spread of the disease to other plants.

Botrytis Blight

Especially if the season is wetter than normal, botrytis blight can cause flowers to develop brown spots that expand and spread to other branches of the plant. The blooms eventually turn fully brown and curl up, then become covered with a fluffy mold, which is why botrytis blight is also called gray mold. When the flowers fall onto leaves on lower branches, the leaves can also develop brown spots, curl up and die. Pruning off diseased stems quickly can help stop the disease, as can spraying a copper fungicide on the hydrangea. Try to water the hydrangea at ground level to keep the leaves and blooms dry to help prevent the spread of the mold.

Mites

Mites tend to munch on the outer edges of oakleaf hydrangea leaves, making the leaves turn brown around the edges. As the infestation grows, the leaves develop multiple brown spots and begin to wilt. This is most noticeable on newly forming leaves, and it can affect bloom growth as well. New blooms may appear discolored or stunted. Mites often leave webbing on the underside of leaves to hold their eggs, which might be the only visible sign of the small bugs. Keeping the hydrangea well watered and fertilized can help it survive a mite infection. You can also spray the plant with a miticide, although these tend to control the problem for only a short amount of time before a reapplication is needed.

About the Author

Based outside Atlanta, Ga., Shala Munroe has been writing and copy editing since 1995. Beginning her career at newspapers such as the "Marietta Daily Journal" and the "Atlanta Business Chronicle," she most recently worked in communications and management for several nonprofit organizations before purchasing a flower shop in 2006. She earned a BA in communications from Jacksonville State University.